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IEEE 802 Tutorial: Video over 802.11 Presenters: Ganesh Venkatesan (Intel) Alex Ashley (NDS) Ed Reuss (Plantronics) Todor Cooklev (Hitachi) Contributors Ganesh Venkatesan, Intel Corporation Alex Ashley, NDS Ltd. Ed Reuss, Plantronics Yongho Seok, LG Electronics Youjin Kim, ETRI

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IEEE 802 Tutorial: Video over 802.11

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Ieee 802 tutorial video over 802 11 l.jpg
IEEE 802 Tutorial:Video over 802.11

Presenters:

Ganesh Venkatesan (Intel)

Alex Ashley (NDS)

Ed Reuss (Plantronics)

Todor Cooklev (Hitachi)


Contributors l.jpg
Contributors

  • Ganesh Venkatesan, Intel Corporation

  • Alex Ashley, NDS Ltd.

  • Ed Reuss, Plantronics

  • Yongho Seok, LG Electronics

  • Youjin Kim, ETRI

  • Emre Gunduzhan, Nortel

  • Harkirat Singh, Samsung

  • Todor Cooklev, Hitachi America Ltd.

  • Sudhanshu Gaur, Hitachi America Ltd.

  • Graham Smith, DSP Group

  • Joe Kwak, InterDigital

  • Don Schultz, Boeing

  • Paul Feinberg, Sony


Outline l.jpg
OUTLINE

Motivation.

Why? - Use Cases

Challenges.

What? - Video and its characteristics

How? - current 802.11 mechanisms

Further work

Limitations in the current 802.11 mechanisms

Possible areas of work

Activities outside 802.11

Conclusions


Motivation use cases l.jpg
Motivation: Use Cases

Flexibility of not having to deal with wires is a compelling reason to use 802.11 for video streaming

Video Streaming encompasses a broad range of use cases

This tutorial will focus on a subset of use cases

Solutions to improve performance for use cases at one end of the spectrum may not be effective to those at the other end


Use case dimensions l.jpg
Use case dimensions

  • Uncompressed or Compressed*

  • Unicast, Simulcast, Simulcast w/data, Multicast or Broadcast

  • Low resolution, standard definition, High Definition, studio quality

  • Resource considerations at the renderer (power, CPU, memory)

  • Source from Storage (DVD), realtime, Interactive, time-shifted content, location-shifted content

  • Dense versus Sparse video networks

  • Audio/Video rendered on the same device or Audio is rendered at speaker(s) wirelessly connected to the video renderer.

  • DRM (content encrypted) or no-DRM (content unencrypted)

* Uses Cases of interest in the tutorial


Use cases l.jpg
Use Cases

Projector

Home theater

(AV receiver)

Wireless AP

(Internet gateway)

DTV

Camcorder

Home PC

Digital camera

STB (Cable TV access)

DVD player

PMP

  • Many applications including …

    • Delivering multiple HD streams to several receivers

    • Displaying stored digital contents from media servers to display devices

    • Browsing contents in distributed devices through big screen TVs


Use cases multicast l.jpg
Use Cases: Multicast

Laptop PC

Laptop PC

Home PC

STB (Cable TV access)

AP

PMP

PMP

PMP

PMP

  • Content server multicasts multimedia streams to many authenticated users.

  • Regardless of how many users receive the streams, a single WLAN channel is expected to be used.

  • Content server can be STB, PC, AP, or even any portable devices.


Use case row of houses l.jpg
Use Case: Row of Houses

Brick construction

2 Compressed Audio/Video Streams

HD or SD

Typically two hops per stream

AP possibly in different room

Additional bandwidth for one voice call and moderate data traffic

Random bursty BE traffic


Use case multiple occupancy dwelling l.jpg
Use Case: Multiple Occupancy Dwelling

  • Apartments in a high-rise setup

    • Brick outer construction, concrete floors, drywall inner

  • 2 SD Audio/Video Streams or 1 HD stream

  • Typically two hops per stream

  • Additional bandwidth for one voice call and moderate data traffic

9


The usage model for tv is very different from the usage model for the internet l.jpg
The usage model for TV is very different from the usage model for the Internet

94 %

8 hours

66 %

42%

33 minutes

TVs are viewed typically for longer hours per day

Video over wireless experience should be comparable to the current experience over ‘wired’ connection(s)

From – The challenges for Broadcast Television over Wireless in-home networks, Alex Asley and Ray Taylor, NDS Ltd. U.K.

Percentage of homes

Hours per day

USA

Ireland

Internet

Television


Use cases typical requirements l.jpg
Use Cases – Typical Requirements model for the Internet


Motivation for video over 802 11 l.jpg
Motivation for video over 802.11 model for the Internet

  • The number of homes with TV is greater than the number of homes with Internet

  • The average US home has 3 TVs

  • 802.11 must work when every home is simultaneously using their network

  • People are used to high-quality video

  • The potential market is huge


What is video not all bits are created equal l.jpg
What is video? model for the InternetNot all bits are created equal

Intra (I) frames, Predicted (P) Frames or Bidirectional (B) Frames.

MPEG-2 typically uses one I-frame followed by 15 P/B frames to make up a GOP.

Video Sequence

Group of Pictures (GoP)

Slice

Macroblock

Picture (Frame)

Block (8x8 pixels)


Slide14 l.jpg

Transport Stream model for the Internet


Slide15 l.jpg

One TS contains audio, video, data model for the Internet

TS Header (4 bytes) has an adaptation field control. This is used among other things to identify the presence of PCR (Program Clock Reference) following the header.


Slide16 l.jpg

How big are video frames? model for the Internet

Y-axis – frame size in bytes


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From video frames to 802.11 packets model for the Internet

  • Video frames typically span multiple 802.11 packets

  • TS header may contain PCR – critical for keeping audio/video in sync

    • if lost, quality suffers dramatically

  • The effect of 802.11 packet loss is different depending upon its contents


How are the metrics defined l.jpg
How are the metrics defined? model for the Internet

  • Rendered Video Quality Metrics (e.g. Mean Opinion Score)

  • Network performance Metrics (Packet Loss, End-to-End Delay)

  • Link Metrics (PER, throughput)

  • With Video –

    • For a given set of network performance metrics it is not easy to predict what the corresponding Video Quality Metric would be

    • For the same set network performance metrics depending on the content of the video stream, the rendered Video Quality Metric could be different

Network

Rendered Video

Video Content


Video bitrates l.jpg
Video Bitrates model for the Internet

  • Constant Bit-rate (CBR)

    • Constant when averaged over a short period of time (e.g. 500ms)

    • Per-picture adaptation of encoding parameters to maintain bitrate

    • Stuffing used to fill to required bitrate

  • Variable Bit-rate (VBR)

    • Variable when averaged over a short time

    • Tends to produce less variable picture quality (complex scenes can use higher bitrates)

  • Statistical Multiplexing

    • A version of variable bitrate encoding when multiple streams are placed inside a constant bitrate channel

    • Bitrate is allocated to each stream based on encoding demands of each stream


Packet loss l.jpg
Packet loss model for the Internet

  • If one packet is lost this will affect other correctly received packets

  • Therefore the propagation effects of a packet loss can be significant

  • Single packet error typically corresponds to the loss of a small frame (P/B) or the loss of a part of a big frame

  • Burst packet loss – significant degradation


Slide21 l.jpg

Parameters* model for the Internet

Max duration of an error event <= 16 ms; 1 error event per 4 hours

Max video/audio delay < 200/50 ms; max jitter < 50 ms

21

* From TR-126 www.dslforum.org


Why is video a unique problem l.jpg
Why is video a unique problem? model for the Internet

As a result of compression:

Highly variable bit rate

Inter-frame data dependency

Some frames are more important than others

Sensitivity to loss and delay

However the effect of packet loss is content-dependent

Resiliency to bit errors

Error concealment can be used

22


Video over wireless challenges l.jpg
Video over Wireless Challenges model for the Internet

Hey, it is wireless

Interference, path loss

Limited number of channels in unlicensed bands

Channel characteristics constantly change (dynamic)

Medium access non-deterministic (802.11 is originally designed for data)

STA physically moves in the same BSS

Inter-stream synchronization

Between audio rendered at remote speakers and video

Between one video stream and multiple audio streams


Current 802 11 mechanisms l.jpg
Current 802.11 Mechanisms model for the Internet

Distributed medium access (EDCA)

prioritization

Centralized medium access (HCCA)

admission control and bandwidth reservation

Direct Link

Dynamic channel selection (802.11h)

RRM/Management (802.11k/v)

HT (802.11n)

PHY techniques for improved robustness


802 11k v features for video l.jpg
802.11k&v Features for Video model for the Internet

  • 11k: Frame Request/Report identifies STAs/APs (channel survey).

  • 11k: Location (LCI) Request/Report may provide location information to sort STAs into in-home or external.

  • 11k: Noise Histogram and Channel Load

  • 11v: Extended Channel Switch permits relocating BSS to selected channel (selection based on channel survey).

  • 11k: Link Measurement and Beacon Request/Report characterize initial link quality in terms of signal level (RCPI) and SNR (RSNI) for video stream at setup time.


802 11k features to monitor quality l.jpg
802.11k features to monitor quality model for the Internet

  • 11k: Transmit Stream Measurement Request/Report for direct video stream monitoring using triggered reports (alerts) on transmit stream MSDU retries, discards, failures or long delay.

  • 11k: Link Measurement Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for STA to STA streams.

  • 11k: Beacon Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for AP to STA streams with conditional reporting (alerts).

  • 11v: Presence Request/Report may detect onset of motion of transmitting or receiving STA to indicate changing link conditions.


Limitations in current 802 11 mechanisms l.jpg
Limitations in current 802.11 mechanisms model for the Internet

Limited prioritization

Lack of inter-layer communication

Limited set of QoS parameters

Limited capability to dynamically tweak QoS parameters

Lack of content-specific methods


Possible areas of work l.jpg
Possible areas of work model for the Internet

MAC-level techniques

Selective Repetition to mitigate packet loss

Smart packet drop

Finer prioritization among streams and within one stream

Content-specific methods

QoS policy (establishing, monitoring, adaptation)

Inter-Layer communication (Vertical interaction)

PHY-MAC

MAC-higher layers


Possible solutions illustration l.jpg

Other data model for the Internet

MPEG2 Packetized Audio Elementary Stream

MPEG2 Packetized Video Elementary Stream

PHY frame

MAC frame

PHY frame

MAC frame

Possible solutions: Illustration

MPEG2 Packetized Transport Stream

  • Dynamic QoS

  • Finer granularity priority levels

  • Content aware protection, transmission, retransmission, etc.

  • Content-aware PHY adaptation

  • Beamforming / STBC

  • Coding / Modulation, etc.


Multiple priority levels l.jpg
Multiple Priority Levels model for the Internet

Inter-stream and Intra-Stream priorities

Real-time video has different QoS requirements compared to stored media.

Current standard has provision for video access category and provides one service to all kinds of video including real-time video, stored media etc

Possible scope for improvement

Use different set of channel access parameters to differentiate premium content, real-time, stored media content

For example, more granular control of AIFSN can be used to differentiate video streams

30


Content aware techniques l.jpg
Content Aware Techniques model for the Internet

Some video frames are more important than others (I > P > B frames)

Current MAC/PHY layers don’t differentiate among different frames

Possible content-specific methods

MAC Layer

Frame based retry limits, fragmentation size, QoS parameters

As a result of PHY/MAC communication:

Frame based FEC coding, modulation scheme, 802.11n specific features such as STBC, Beamforming etc.

31


Do fec do not check crc l.jpg
Do FEC, do not check CRC model for the Internet


Related activity outside 802 11 l.jpg
Related activity outside 802.11 model for the Internet

  • CEA R7 Home Network Group

  • IETF Audio/Video Transport (AVT) Working Group

    • Specification of a protocol for real-time transmission of audio/video over unicast/multicast UDP/IP

    • RTP/RTCP

  • ISO (MPEG-2/4)

  • ITU-T Video Coding Experts Group (VCEG)

  • DLNA uPnP

  • Other

    • Video over cellular networks

    • Video over DSL, cable, powerline, etc.


  • Conclusions l.jpg
    Conclusions model for the Internet

    • Video is different from data; existing 802.11 mechanisms are not sufficient

    • The home networking industry at present is not planning to use 802.11 for video distribution!

      • Instead, cable or powerline are being used

    • 802.11 will be the medium of choice only if more is done in a timely fashion.

      The industry is ready for 802.11 based Video Streaming NOW.


    Some references l.jpg
    Some references model for the Internet

    • ISO MPEG2 standard and ITU equivalents H.261, H. 262, H. 264

    • HDMI

    • ITU-R BT.656 and BT.470-5

    • 3GPP Techniques to transport sub-streams – Advanced Multi-Rate encoding, specifications 26.091 V6.0.0, 26.101 V6.0.0 and 26.102 v7.1.0, www.3gpp.org

    • TR-126 (http://www.dslforum.org/techwork/tr/TR-106.pdf)

    • MediaFlo, FloTM Technologies by Qualcomm

    • http://www.compression.ru/video/quality_measure/index_en.html

    • There have been a number of 802.11 WNG presentations, 11-05-0910-01-0wng, 11-06-0039-01-0wng, 11-06-0360-00-0wng contain more references


    Backup l.jpg
    Backup model for the Internet


    Slide37 l.jpg

    Video Characteristics model for the Internet

    GOP Size (bytes)


    11n use cases application specific details doc ieee 802 11 03 802r23 l.jpg
    11n use cases: application specific details ( model for the Internetdoc.: IEEE 802.11-03/802r23)


    Packet loss not all packets are born equal l.jpg
    Packet Loss: Not all packets are born equal model for the Internet

    Single I-frame IP packet loss

    (14 frames affected)

    Single B-frame IP packet loss

    (1 frame affected)

    Furthermore the loss of an IP packet can mean the loss of a PES header or a loss of a timestamp at the TS or PES layer. The worst case for losing an IP packet causes loss of 0.5 seconds worth of video.

    Source – TR126, www.dslforum.org


    Error concealment at the renderer l.jpg
    Error Concealment at the renderer model for the Internet

    Error concealed using a simple average of Macro Blocks around the region corresponding to lost data

    No Error Concealment

    From “Error Concealment Techniques for Digital TV by Jae-Won Suh and Yo-Sung Ho, IEEE TRANSACTIONS ON BROADCASTING, VOL. 48, NO. 4, DECEMBER 2002, Pages 299-306.


    Resiliency to bit errors l.jpg
    Resiliency to bit errors model for the Internet


    Limitations in current 802 11 mechanisms qos edca tspec admission control l.jpg
    Limitations in Current 802.11 Mechanisms (QoS + EDCA TSPEC Admission Control)

    Delay variation

    Throughput variation

    From “Evaluation of Distributed Admission Control for the IEEE 802.11e EDCA by Yang Xiao and Haizhon Li, University of Memphis, IEEE Radio Communications, Pages S20-S24”


    Qos policy needs to be dynamic l.jpg
    QoS policy needs to be dynamic Admission Control)

    Establishing QoS contract with QoS parameters

    Monitoring the established contract

    Channels may changing

    The behaviour of admitted streams can change

    Based on the monitoring, the capability to take appropriate actions should be provided

    A good service may offer tiered QoS, for gradual degradation.

    e.g. the transmitter may support variable bitrate output

    There may be multiple content contributors.

    Cable TV provider may be responsible for video delivery

    Telco may be responsible for Telephony

    Consumer may have purchased the home networking infrastructure


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